The present invention relates to a defect detecting apparatus for sensitively and fast detecting minute extraneous substance or defects existing on semiconductor substrates.
The production lines for semiconductor substrates or thin film substrates examine for the foreign matter deposited on the surfaces of semiconductor substrates or thin film substrates in order to observe the dust-covered condition of the manufacturing apparatus. For example, any semiconductor substrate with circuit patterns not formed yet is subject to the test of if a minute foreign substance or defect of 0.1 μm or below is detected on its surface. There are prior arts for detecting very little defects on samples of semiconductor substrates as disclosed in U.S. Pat. No. 4,601,576 and U.S. Pat. No. 5,798,829. In these documents, a laser beam collected, or focused to a few tens of micrometers μm is irradiated on the sample surface, detects the scattered light from the foreign matter adhered or defect on the semiconductor substrate, and tests if there is a foreign substance or defect over the entire sample surface by rotating the sample and feeding it straight.
Since the irradiated laser beam usually has a Gauss distribution 201 as shown in FIG. 16, the beam irradiation density depends on the relative position of the existing foreign matter/defect to the irradiation position. That is, the scattered light intensity from even the same foreign substance/defect varies as indicated by detected signals 202, 203 and 204. The precision with which the test sample is placed and set on the sample stage is within the range from a few tens of μm to several hundreds of μm. The size, or diameter of the laser beam is similarly in the range from a few tens of μm to several hundreds of μm. Therefore, the relative position of the defect/foreign matter to the beam irradiation position changes each time the test is made, and thus the detected signal from the same foreign matter/defect varies. Accordingly, the reproducibility of the test is reduced. In addition, there is another prior art of U.S. Pat. No. 6,295,168 in which a construction for the test is disclosed.
The defect detecting apparatus for detecting the foreign matter/defect from the scattered light from the sample surface by focusing/irradiating a laser beam on the surface of the test sample can be adapted to prevent the reproducibility from lowering due to the Gauss distribution of the laser beam and to stably detect the foreign matter/defect.